Well surveying method and apparatus



Nov. I7-, 1942.

J- NEUFELD WELL SURVEYING METHOD AND APPARATUS Filed April 22, 1940Patented Nov. 17, 1942 asumirA WELL SUBEYING METHOD AND APPARATUS JacobNeufeld, Tulsa, Okla., asslgnor to Well Surveys, Incorporated, Tulsa,Okla., a corporation of Delaware Application April 22, 1940, Serial No.331,038

(Cl. Z50-83.6)

7 Claims.

'I'his invention relates to geophysical prospecting and moreparticularly to an improvement in that type of geophysical prospectingthat comprises bombarding subsurface strata, in situ, with neutrons orsimilar deeply penetrating radiations and measuring the resultantscattered, reflected, induced or secondary radiations.

In application 239,781 led November 10, 1938, by Robert E. Fearon amethod is described of determining the nature of subsurface strata bybombarding the strata with neutrons or the like and measuring the gammarays returned to a point nearby. Various improvements upon this methodand further advances along the same general line are described in thefollowing applications flled by the same inventor: Serial Nos. 325,880,March-25, 1940; 323,981, March 14, 1940; and 326,510, March 28, 1940.Patent No. 2,133,776 granted to John C. Bender on October 18, 1938 alsodiscloses a method of this general type.

'I'he present invention is an improvement that is applicable to anymethod of this type and the main purpose of this improvement is to avoidmuch of the heavy shielding that is necessary to prevent neutrons or thelike from passing directly from the primary source to the detector andthus producing an error in the measurements The invention also providesa way of controlling the neutron bombardment so that it is concentratedin a particular direction where it will be most effective for thepurpose of causing radiations for the desired measurements.

If an attempt is made to accomplish this result by merely shielding asource of neutrons so that the neutrons can escape only in the desireddirection much diiliculty is encountered because neutrons are verypenetrating and relatively great thicknesses of `shielding are necessaryto stop them effectively. Since the instruments in which these sourcesof neutrons are to be used are necessarily of relatively smalldimensions so that they can be lowered into a bore hole the problem ofproviding sufilcient shielding is unusually difiicult.

It has now been discovered that this dimculty may be overcome by the useof a source of alpha radiations Y, and a material that will generateneutrons upon lbeing radiated with alpha radiations, if the source ofalpha radiations is so arranged and shielded that the alpha radiationsimpinge on the neutron generating source only in the direction in whichit is desired to have i the generated neutrons travel.

Paris, 1935, page 376, if thealpha radiations are directed from asuitable source onto a material that will generate neutrons uponexposure to alpha radiations, most of the neutrons emitted will travelin the direction in which the alpna radiations are traveling when theystrike the neutron emitting material.

It so happens that alpha radiations have very little penetrating powerand hence a source oi alpha radiations can be easily shielded. Now, ifthe source of alpha 4radiations is shielded so that the alpha radiationsare allowed to fall on a neutron generating material such as berylliumor boron, only from a single direction, then the neutrons, for the mostpart, will be emitted in that direction.

Following these principles, a device may be made for lowering into awell, which device will contain a detector of returning radiations and agenerator of primary radiations. The generator may consist of a materialthat will emit neutrons and a source of alpha radiations so arranged asto radiate this source of neutrons with alpha radiations traveling forthe most part in such a direction that the resultant 4neutrons will bedirected outwardly away from the detecting instrument at just the properangle so that they will have no substantial eiect on the detectinginstrument themselves but will have a maximum eiect in generatingsecondary radiations at the desired place or in being scattered andreturning to the measuring instrument.

For a more complete understanding of the details and advantages of thisinvention reference may be had to the appended drawing in which the solegure shows diagrammatically a simple form of measuring instrumentconstructed according to the principles of lthis invention.

As illustrated, a detecting instrumentV according to the principles ofthis invention may consist of al cylindrical housing I0 suspended fromthe surface by means of a cable Il, which also carries conductors forconveying a measurement indicating current to-the surface. Within thecylindrical housing, which incidentally is sealed so that the uids inthewell bore cannot enter it, there may be positioned a detecting unit anda unit for generating primary radiations.

The detecting unit may consist of an ionization chamber I2 containing apair of electrodes I3 and i4 and illled with an inert gas such as argonunder a pressure of around 1500 to 2000 pounds per square inch. Theelectrodes are preferably a cylindrical iron rod and a surroundingcylindrical iron shell.

Connections from the electrodes are carried through the chamber wall ininsulated bushings and a. resistor I5 and a battery I6 are connected ofthe chamber. The resistor preferably has a resistance of around 1012ohms and the battery a Voltage of around 15G-volts. The voltagedeveloped across the resistor will be proportional to the current whichflows in the circuit and is governed by the state of ionization of thegas in the ionization chamber which in turn is controlled by theradiations passing through it. Across the resistor I5 there ispreferably connected an amplier I'I which generates a currentproportional to the voltage across the resistor and sends this voltageto the surface through the cable II.

The recording equipment on the surface is of the same general nature asthat described in the applications mentioned in the first part of thisspecification and hence has not been illustrated and will not bere-described here in detail. It consists of a means for raising andlowering the casing I0 inthe well and for recording the currents fromthe amplifier I 'I in correlation with determinations of the position ofthe casing at the time when the currents are generated. By

- continuous operation of the device a continuous being bombarded withalpha particles may also be used.

Within the ring and at a position s uch that 4in series across theelectrode terminals outside of the neutrons generated will have anytendency to pass directly to the ionization chamber.

As has been already stated the device may be modif-led or changed in anyone of the great number of Ways without departing from the principlesofv this invention. Also'it can be used either in cased or uncasedwells. It is to be understood therefore that the scope of this inventionis limited only Within the scope of the accompanying claims.

I claim:

1. In a device for geophysical vprospecting which includes a source ofprimary radioactive its radiations will fall on the ring in a directionthat is outwardv and somewhat upward from the source is a source 'ofalpha particles I9. This source may be radon, mesothorium, radiothoriumor any other material that will give off alpha particles in sufficientquantities to cause the desired production of neutrons. Above and belowthe source of alpha particle source there may be arranged shields 20 and2| which prevent the alpha particles from traveling in directions inwhich they will not be useful.

By arranging the source of alpha particles so that the alpha particlestravel upwardly and outwardly to the neutron generating material, theneutrons that are generated are also caused to travel outwardly andupwardly so that they pene,- trate out into the surrounding stratarather than upwardly toward the detecting instrument. At the same timethey are caused 'to pass into the surrounding strata at a place wheretheir action onthe surrounding strata will have the greatest possibleeffect in causing radiations -to return to the measuring instrument.

For the purpose of illustrating this fact dotted lines are shown in thedrawing, indicating the radiations and a detector for detectingradiations that result in the bombardment of formations underinvestigation with said primary radiations, the improvement thatcomprises as a source of said primary radioactive radiations a materialthat emits said primary radioactive radiations upon being bombarded withless penetrating radiations,. source of said less penetrating radiationsand means to shield said source of less penetrating radiations so thatsaid less penetra ing radiation bombards said source of prima radiationsubstantially only in a predetermined direction.

2. In a method of geophysical prospecting in which formations to beinvestigated are bombarded by a source of primary radioactive radiationand radiations emerging from said formations as a result are measured,the improvement that comprises generating said primary radioactiveradiations from a material capable of producing said primary radiationsby bombarding said material with less penetrating radiations whiledirecting said less penetrating radiations so that the primaryradiations lwhen generated are directed, for the most part, into theformation and not toward the detecting point.

V3. In a method of geophysical prospecting in which formations to beinvestigated are bombarded with neutrons and the gamma rays emitted fromthe formations as a result thereof are measured, the improvement thatcomprises generating theA neutrons by bombarding a material with alphaparticles which material will' generate neutrons upon such bombardment,and directing the bombarding alpha particles so that they striketheneutron emitting material in a direction that will cause the neutrons,which are emitted in the same direction to pass into the formation beingstudied rather than toward the point at which gamma rays are detected.

4. In a device for Ageophysical prospecting which includesga source ofneutrons and a detector for detecting gamma rays emitted from theformations bombardedV with said neutrons, the improvement that comprisesutilizing as a means tol generate said neutrons, a substance that willemit neutrons upon being bombarded by alpha particles and a sourcel ofalpha particles so placed j in relation to said neutron emittingsubstance path of the major portion of the emitted neu.

trons and the path of thev returning radiations It willv that the alphaparticles will 'strike the neutron emitting substance in a directionsuch as to drive the neutrons into the formation under investigationrather than towards the point at which the returning gamma rays aredetected.

5. In a device for geophysical prospecting which includes a casingadapted to be lowered into a well bore and containing a source ofneutrons and an instrument for detecting gamma rays which return fromthe surrounding formations as the measuring instrument and yet that veryfew uiV a result ofV their being bombarded with the neutrons, Vtheimprovement comprises as a means to generate neutrons a materialthatwill generate ing generally toward the formations Surroundl ing themeasuring part of the instrument so that the neutrons will be emitted inthat same general direction instead of toward the measuring inyStrument.

6. In a geophysical prospecting device, a directional primary radiationsource that comprises a mass of material capable of emitting a rst typeof radiation when subjected to a second type of radiation and adirectionalrsource of said Vsecond type of radiation disposed totransmit its radiation in the direction of the intended path of saidfirst type of radiation.

7. In a geophysical prospecting device of the type that includes asource of a irst type of radiation for bombarding geological formationsunder investigation and a detector for radiation emanating from theformations, the improvement that comprises a mass of material capable ofemitting said rst type Vof radiation when subjected to bombardment witha second type of radiation and a. directional source of said second typeof radiation disposed to transmit its radiation in the direction of theintended path of said rst type radiation.

JACOB NEUFELD.

